1. Field of the Invention
The present invention relates to a lubricating composition.
2. Description of the Related Art
Recently, automobile regulations such as regulations regarding fuel consumption and exhaust emissions have become more and more severe. The reasons behind this are environmental problems such as air pollution, acid rain and the like, and protection of resources out of a concern for depletion of finite petroleum energy. As a counter measure, reducing fuel consumption is the most effective solution at present.
When reducing automobile fuel consumption, i.e., when improving fuel consumption, improvements in engine oils such as lowering engine oil viscosity in order to reduce engine frictional loss, adding good friction regulators or the like are just as important as improvements in the automobile itself such as lightening automobile bodies, improvements in engines, etc. Although engine oil acts as a lubricant between pistons and liners, this is where there is a lot of fluid lubrication. So lowering engine oil viscosity can decrease frictional loss. However, even though lowering engine oil viscosity has proposed in recent years, lowering the viscosity causes problems such as defective sealing and increased wear. Engine oil plays an important role in lubricating valve gear, bearings and the like where mixed lubrication and boundary lubrication are mostly employed. Therefore, lowering the viscosity of the engine oil causes increased wear. Friction regulators, extreme pressure agents or the like are added thereto in order to decrease the friction loss and prevent the wear that accompanies a lowering of engine oil viscosity.
Generally, organic molybdenum compounds are added to different types of lubricant oil due to their excellent friction reducing properties. Such compounds are especially effective in engine oils for reducing fuel consumption, which makes them an essential additive for fuel consumption reducing oils. Even though fuel consumption reducing oil shows excellent properties when new, this is not sufficient for excellent fuel consumption reducing oil. Excellent fuel consumption reducing oil must keep their fuel consumption reducing properties for long periods of time. Accordingly, an important theme for current fuel consumption reducing oils is whether the friction reducing effect can be maintained for a long period of time.
Among the organic molybdenum compounds having excellent fuel consumption reducing properties, molybdenum oxysulfide dialkyldithiocarbamates are the most notable ones. These compounds have been known as lubricants for a long time. For example, Japanese Patent Publication No. 53-31646 describes that molybdenum oxysulfide dialkyldithiocarbamate having alkyl groups containing 1 to 24 carbon atoms and containing a sulfur atom and an oxygen atom at a specific ratio is used as a lubricant. Japanese Patent Publication No. 6-47675 discloses molybdenum oxysulfide dialkyldithiocarbamate having asymmetric alkyl groups to improve its solubility to a base oil.
The above-described organic molybdenum compounds are mainly used in gasoline engine oils, and various blends thereof have been developed. On the other hand, where the organic molybdenum compounds are blended into diesel engine oils, there are problems in that the organic molybdenum compounds cannot sufficiently exercise their properties as compared to when they are blended into gasoline engine oils. There are many differences between gasoline engines and diesel engines. A significant factor that affects engine oil is soot. In diesel engines, it is found that soot is produced by combustion and enters into the diesel engine oil.
However, dispersants are added to engine oils to disperse sludge that enters that way. Japanese Patent Laid-open Nos. 10-183153 and 11-21278 describe that alkenyl succinimide-based compounds having specific properties are suitably used for diesel engines.
The present inventors have assumed that soot is the cause of the organic molybdenum compounds not exhibiting sufficient effectiveness in diesel engines and have attempted to blending in various additives into them. As a result, they have successfully developed a lubricating composition that can exhibit excellent fuel consumption reducing properties not only in gasoline engines but also in diesel engines by using a succinimide compound having specific properties with the organic molybdenum compound.